xfrm: espintcp: fix UAF during close

commit deb232e884877bf10b4ce2580909eedec986c284 upstream.

ZDI reported and analyzed a race condition during close for espintcp
sockets:

    espintcp_close() frees emsg->skb via kfree_skb() without holding
    any socket lock. Concurrently, the xfrm_trans_reinject work queue
    invokes esp_output_tcp_finish() -> espintcp_push_skb() ->
    espintcp_push_msgs() -> skb_send_sock_locked(), which reads the
    same skb as a data source.

Fix this by adding a synchronize_rcu() call after resetting sk_prot,
since esp_output_tcp_finish() runs under RCU and won't use a socket
with sk_prot == &tcp_prot.  Simply taking the socket lock in
espintcp_close() could lead to leaks, if esp_output_tcp_finish()
re-adds an skb in the slot we just freed. After this, the existing
barrier() is no longer needed.

Cc: stable@vger.kernel.org
Fixes: e27cca96cd68 ("xfrm: add espintcp (RFC 8229)")
Reported-by: zdi-disclosures@trendmicro.com
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/xfrm/espintcp.c b/net/xfrm/espintcp.c
index dd7a7dc027855329f4dd0493e0b4fd6972cd5713..84e9412066b3b1c14a9d903be003a152199c530d 100644 (file)
--- a/net/xfrm/espintcp.c
+++ b/net/xfrm/espintcp.c
@@ -518,7 +518,8 @@ static void espintcp_close(struct sock *sk, long timeout)
        strp_stop(&ctx->strp);
 
        sk->sk_prot = &tcp_prot;
-       barrier();
+
+       synchronize_rcu();
 
        disable_work_sync(&ctx->work);
        strp_done(&ctx->strp);